Wettable fiber felt



United States Patent WETTABLE FIBER FELT Donald E. Dahle, Birmingham, Mich, assignor to Wood Conversion Company, St. Paul, Minn., a corporation of Delaware No Drawing. Application June 8, 1951, Serial No. 230,700

6 Claims. (Cl. 128156) The present invention relates to air-laid fiber felts of fibers inherently absorbent of aqueous liquid, and in particular to such felts in sheet form having wet-strength to resist disintegration when wet as a result of absorption of aqueous liquid.

In particular, the invention relates to the incorporation in the felt in the air-laying. process of an agent serving to accelerate the absorbency 'of the fibers.

Heretofore, air-laid fiber felts have been made from many kinds of fibers, particularly those derived from wood, in various forms of refinement toward cellulose, for example, sulfite wood fibers. The fibers are individually suspended in air and then deposited therefrom in the form of a felt. The deposition may be'efiected in numerous ways, among them filtration onto a continuously moving screen by differential pressure, and also by deposition on a moving conveyer by gravity fall from dispersion in a deposition chamber.

The fibers as first suspended in air are substantially dry to permit use of mechanical apparatus including conduits and the like, without fouling the equipment with wet fiber. It is also customary where a bonding agent is employed'to use an aqueous liquid binder in a suitable manner applying it to the fibers before, at, or immediately after deposition of the fibers while the felt is being formed. Such liquid binder permits the resulting moist felt being formed to contain mobile fibers, thus to permit additional felting by compression, or other rearrangement as required, before the moist felt is dried to set the bond and integrate the felt.

In gravity deposition a fine mist or spray of such'liquid binder is injected into a deposition chamber, into which the fibers suspended in air are introduced, for expansion in the chamber and settling onto a continuously moving conveyer. In such gravity deposition, some of the mist particles land upon the fibers in suspension and other particles gravitate to the top-most fibers on the mat as it is being'formed. In gravity felting the fibers do not pack well'and the density of the formed mat is so low that the initially formed felt has little strength. Compression of the initially formed mat increases the felting and gives greater density with adequate strength for movement of the felt into a drier. The compression is controlled'to predetermine the density of the dried mat.

Among the binders heretofore employed are hydrophilic materials such as starch, dextrin or gums, and other binders such as thermosetting resin-forming solids, for example, soluble condensation products of phenol and formaldehyde. The latter material on thermal reaction in the drier gives a water-insoluble bond and for that reason is commonly used in sufficient quantity to coat or size the surfaces of the individual fibers of the mat with a thin resin film. So used it seals the fibers against liquid absorption and the absorbent capacity of the resulting mat is largely that of capillarity between the fibers, and not that of the fibers per se. However, when the quantity of such resin is reduced to an amount insufficient to comice pletely' coat the fibers, the inherent absorbency of the fibers is not lost.

When the binder consists of starch, gum or like hydrophilic binder, the dried mat has no wet-strength, being subject to disintegration upon wetting by reason of the bond absorbing the water and losing its binding'quality. Starch or the like does not seal the fibers against absorbing water or liquids as does the greater quantity of phenolformaldehyde' resin binder above mentioned. quently, a starch bound fiber mat" to be used for aqueous absorbency maydisintegrate when subjected to the action of aqueous liquids.- In some uses of absorbent mats, thisdisintegration is not objectionable, but in other uses it is'desired that themat maintain its felted integrity. With starch this may be accomplished by adding a small quantity of a suitable material which is compatible with the hydrophilic binder in aqueous solution and effective in rendering the dried bond resistant to disintegration by water. Among the suitable materials for starch which function by reaction with starch on drying, are dimethylol urea, monomethylol urea, urea formaldehyde, melamine formaldehyde, and potassium pyroantimoniate. (See U. S. Patent No. 2,450,377.) When approximately 10 parts of binder solids'are used for 100 parts of fiber, an aqueous liquid binder having approximately 5% of its solids in the form of dimethylol urea and as starch provides a hydrophilic bond giving the dried mat resistance to disintegration-when Wet.

However, a binder consisting of starch, or of dimethylol urea and starch, functions as a size on the surface of the fibers which'retards absorbent action of the mat when exposed to liquids to be'absorbed thereby. There are many uses where high quality and low-cost fiber cushions are desired with absorptive capacity for aqueous liquids, and with. rapid rather than retarded absorptive characteristics. Such uses are exemplified by packaging and packing material, for example, for bottled liquids and the like, hospital mattress covers or pads, surgical packings and dressings, and sanitary napkins. In static uses the possibility of disintegration is generally not important, but where the absorbing mat is subject to movement, wetstrength is most desirable.

It is the object of the present invention to produce airlaid absorbent fiber felts integrated by a hydrophilic bonding agent in kind or quantity which does not seal-01f the absorbency of the fibers and to incorporate in the mat as it is being formed a wetting agent for accelerating or controlling the rate of absorption in accordance with specific requirements.

It is also an object of the invention to subject'an air suspension of water-absorbent fibers to be formed into a bound mat to contact with finelyv divided liquid binder and with a finely divided solution of a wetting agent for distributing the latter throughout the mat.

It is a particular object of the invention to combine the bonding agent and the wetting agent in one solution and to direct it'as a fine mist toward the suspended fibers for deposit thereon or on the fibers being felted.

Various other and ancillary objects and advantages of the invention will be apparent from the following description and explanation of the invention.

In numerous experiments with dry mats formed by gravity deposition from sulfite fibers, using a solution containing about 10 parts of binder to parts of fiber, where the binder is primarily starch with or without a small quantity of dimethylol urea, it has been found that the binder retards the absorption of aqueous liquid compared to the inherent rate of absorption of the fibers per se. However, the total absorption capacity of the mats bound with starch or with starch plus the dimethylol urea, is the same as that of the fibers per se, with the difference residing in the rates of absorption and in the Patented Mar. 6, 1 956 Conse-,

integrity of the mat after absorption. The present invention is based upon the discovery that inclusion of a suitable wetting agent increases the rate of absorption without adding to the capacity for absorption. Thus, by controlling the amount of wetting agent in any particular type of bound mat, the rate of absorption of the mat may be controlled for particular uses.

Among the vegetable fibers which may be used in the present invention are sulfite or soda pulp from wood or other lignocellulose, cotton, bagasse, ramie, rayon, groundwood and the like.

The binder solids employed in aqueous liquid form range from to parts by weight to 100 parts of fiber, and preferably 8 to 10 parts. Where a resisting agent is used, such as those mentioned and preferably dimethylol urea in the case of starch binder, the agent may vary by weight from 5 to parts per 100 parts of starch. The wetting agent may vary over a wide range of organic materials, organic quaternary ammonium salts which are water soluble, glycerol, and especially the sodium sulfonates and sulfates of organic compounds, such as the fatty alcohol sulfates. In general these compounds are called surfactants, and they may be cationic, anionic or nonionic.

Typical felts were made by gravity deposition, using 9 the process and apparatus shown in'Heino No. 2,493,194. There were employed 100 parts of dry sulfite fibers and 133 parts of liquid binder containing 6% solids, of which solids 95% was starch and 5% was dimethylol urea. The fibers were initially deposited at a dry weight density of about /2 lb. per cu. ft., then compressed to a dry weight density of 2 lbs. per cu. ft. and dried at about 240 F. In addition there was added to the binder liquid on the basis of parts by weight to 100 parts of fiber, 1 part of a surfactant from the list A, B, C, and D or parts of E, these materials being indicated in the table below.

The dried mats were then tested for rate and capacity of absorbency by Test No. 1 and Test No. 2.

Test No. 1 is to float a weighed piece of the mat on water, for seconds, then to remove it and determine the increase in weight, expressed in Table 1 as a factor converting dry Weight to wet weight.

Test No. 2 is to immerse a weighed specimen of mat in water at a 6-inch head for five minutes, then to release it to sink or float as it will for an additional 55 minutes. The test is reported as a factor converting dry weight to wet weight.

The foregoing shows that the ultimate absorption, or capacity, is not altered by the wetting agent, and that in exposure before capacity is satisfiied, the water is taken up more quickly by the mats having the wetting agent 4 than the mat without it. The fact that the mats in Test No. 2 did not disintegrate is due to the presence therein of the dimethylol urea.

Numerous modifications and variations, not disclosed herein, are contemplated as falling within the scope of the invention hereof as defined in the appended claims.

I claim:

1. An open and porous integral felt of cellulosic fibers which have absorbent capacity for aqueous liquid, a dried and cured hydrophilic binder material on at least some of the fiber surfaces and at fiber junctions bonding the fibers together in the felt, and wetting agent included in generally uniform distribution throughout the felt, the binder material comprising per 100 parts by weight of fiber from 5 to 15 parts of the dried residue of a starch sol, and per 100 parts of such starch from 5 to 20 parts of material selected from the group consisting of dimethylol urea, monomethylol urea, urea-formaldehyde, melamine formaldehyde, and potassium pyroantimoniate, the wetting agent being present in an amount of at least 1 part by weight per 100 parts of fiber.

2. The product of claim 1 wherein the wetting agent resides predominantly in binder material.

3. An open and porous integral felt of cellulosic fibers which have absorbent capacity for aqueous liquid, a dried and cured hydrophilic binder material on at least some of the fiber surfaces and at fiber junctions bonding the fibers together in the felt, and wetting agent included in generally uniform distribution throughout the felt, the binder material comprising per 100 parts by weight of fiber from 5 to 15 parts of the dried residue of a starch sol, and per 100 parts of such starch from 5 to 20 parts of dimethylol urea, the wetting agent being present in an amount of at least 1 part by weight per 100 parts of fiber.

4. The product of claim 3 wherein the wetting agent resides predominantly in the binder material.

5. An open and porous integral felt of cellulosic fibers which have absorbent capacity for aqueous liquid, a dried and cured hydrophilic binder material on at least some of the fiber surfaces and at fiber junctions bonding the fibers together in the felt, and wetting agent included in generally uniform distribution throughout the felt, the binder material comprising per 100 parts by weight of fiber from 9 to 10 parts of dried residue of a starch sol, and per parts of starch 5 parts of dimethylol urea, the wetting agent being present in an amount of at least 1 part by weight per parts of fiber.

6. The product of claim 5 wherein the wetting agent resides predominantly in the binder material.

References Cited in the file of this patent UNITED STATES PATENTS 2,212,557 Bauer Aug. 27, 1940 2,256,034 Nottebohm Sept. 16, 1941 2,288,095 Lindsay June 30, 1942 2,339,562 Eustis Jan. 18, 1944 2,359,858 Iler Oct. 10, 1944 2,431,035 Goepfert et al Nov. 18, 1947 2,493,194 Heino Jan. 3, 1950 2,544,714 Moore Mar. 13, 1951 2,610,138 Heritage Sept. 9, 1952 

1. AN OPEN AND POROUS INTEGRAL FELT OF CELLULOSIC FIBERS WHICH HAVE ABSORBENT CAPACITY FOR AQUEOUS LIQUID, A DRIED AND CURED HYDROPHILIC BINDER MATERIAL ON AT LEAST SOME OF THE FIBER SURFACES AND AT FIBER JUNCTIONS BONDING THE FIBERS TOGETHER IN THE FELT, AND WETTING AGENT INCLUDED IN GENERALLY UNIFORM DISTRIBUTION THROUGHOUT THE FELT, THE BINDER MATERIAL COMPRISING PER 100 PARTS BY WEIGHT OF FIBER FROM 5 TO 15 PARTS OF THE DRIED RESIDUE OF A STARCH SOL, AND PER 100 PARTS OF SUCH STARCH FROM 5 TO 20 PARTS OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF DIMETHYLOL UREA, MONOMETHYLOL UREA, UREA-FORMALDEHYDE, MELAMINE FORMALDEHYDE, AND POTASSIUM PYROANTIMONIATE, THE WETTING AGENT BEING PRESENT IN AN AMOUNT OF AT LEAST 1 PART BY WEIGHT PER 100 PARTS OF FIBERS. 